Cell Cycle

Limits to Cell SizeThe Cell Cycle

Regulating the Cell Cycle

Limits to cell size

Why are cells so small? What advantage is there to keep lots of small cells rather than have one large cell?

• Specialization

• Protection and resistance to damage

• Efficiency (surface area:volume ratio)

Cell Size

Surface Area (length x width x 6)

Volume (length x width x height)

Ratio of Surface Area to Volume

Ratio of Surface Area to Volume in Cells

• How far will food particles be able to diffuse into each cell?

• What factors effect transfer of material into/out of the cell?

• How is this used in the human body?

Johnson Exploration: Cell Size

• Cell Maintenance– The work of cells is done by proteins. As a cell

gets larger, more proteins are required to maintain its function.

– If the cell gets too large, DNA instructions cannot be copied quickly enough to make the proteins that the cell needs to support itself.

– Cell size is also limited by the cell’s DNA.

• Exchanging Materials (surface area:volume ratio)

– Oxygen, food, water and wastes all pass through the cell membrane.

– How fast these can enter and exit depend on the external surface area.

– How fast the cell uses food and oxygen depends on the internal volume.

Summary• The larger the cell becomes, the more

demands the cell places on its DNA (DNA overload) and the more trouble the cell has moving enough nutrients and wastes across the cell membrane (surface area:volume ratio).

• Solution: Small cells

Cell CycleCell Cycle

ReproductionImportance link

Asexual- 1 parent

Sexual- 2 parents

• Each time a cell reproduces, it divides into two new cells. When each of the new cells divide, the result is four new cells. If this continues, how many cells will be present after the cells reproduce 6 times?

Exploring Life CD

Problem solving: How important is the fist cell division.

Binary FissionBinary Fission• Bacteria, cyanobacteria, and most

single celled organisms reproduce by binary fissionbinary fission.

DNA

cell membrane

bacteria

• Duplication of a eukaryotic somatic cell.

•• Somatic CellSomatic Cell-- body cell ex. Skin, liver etc. Does not include: sperm or egg.

• All Somatic cells have the same number of chromosomes.

MMIITTOOSSIISS

Liver Cell

2n=46

Results:twoidenticaldaughtercells

Liver Cell

Liver Cell

2n=46

2n=46

G2 phase

S phase

G1 phase

CCEELLL L

CCYYCCLLEE

Cell cycle animationInterphaseInterphaseNormal cell activitiesNormal cell activities

MitosisMitosisDivision of chromosomesDivision of chromosomes

CytokinesisCytokinesisDivision of cytoplasmDivision of cytoplasm

Mitosis

Interphase

G1 phase

S phase

Prophase

G2 phase

Metaphase

Telophase

Anaphase

Cytokinesis

IINNTTEERRPPHHAASSEE

• Comprises about 90% of the cell life cycle.

• What takes place at this time?1. Cellular growth

2. protein synthesis

3. metabolic activities

4. DNA replication (synthesis)

Normal Cell activities

1.1. GG11 (gap) phase:(gap) phase:

– Growth, protein synthesis and metabolic activities. (normal activities)

–– most cell exist in this phasemost cell exist in this phase.

2.2. S (synthesis) phase:S (synthesis) phase:

–– DNA replicationDNA replication

3.3. GG22 (gap) phase:(gap) phase:

– Cellular growth and preparation for MitosisMitosis.

IINNTTEERRPPHHAASSEE

G2 phaseS phase

G1 phase

Problem Solving- how does the cell cycle vary?

InterphaseInterphase

•• NucleusNucleus and nucleolusnucleolus visible.

Nuclear Envelope

nucleolus

cell membrane

chromatin

Question:Question:•• What is a What is a chromosome vs. chromatinchromosome vs. chromatin??

Chromosome

Supercoils

Coils

Nucleosome

Histones

DNA

double

helix

•• ChromosomeChromosome is made up of a DNADNA - histonehistoneproteinprotein complex. Chromosomes have their own centromere.

•• ChromatinChromatin is a long, thin DNA fiber before it is coiled into a chromosome.

Centromere

• A replicated chromosomechromosome consist of two strands of identical DNA called chromatidschromatids (sister sister chromatidschromatids) held together by a centromere.

chromatid

chromatid

S phase: chromosomes replicate

chromosome

chromosome

centromere

What is a replicated chromosome?What is a replicated chromosome?

Answer:Answer:

• A chromatidchromatid is a chromatidchromatid as long as it is held in association with a sistersister chromatidchromatid at the centromerecentromere.

chromatid

chromatid

centromere

chromosome

•• When is a When is a chromatidchromatid a a chromatidchromatid??

chromosome

PPRROOPPHHAASSEE A

B

C

D

E

F

Click to animate the image.

Longest phase of mitosisLongest phase of mitosis

•• CentriolesCentrioles move apart (not found in plants)

•• Spindle fibers Spindle fibers form and attach to centromeres

• Nuclear envelope breaks down, nucleolus disappears

Mitosis: Interactive Java Tutorial

ProphaseProphase

late prophaselate prophaseearly prophaseearly prophase

centrioles

spindle fibers

centromere

nuclear envelopedisappearing

asterfibers

Question:Question:

•• What attaches the What attaches the spindle fibersspindle fibers to the to the centromerescentromeres??

Answer:Answer: KinetochoresKinetochores

sistersisterchromatidchromatid

sistersisterchromatidchromatid

centromerecentromere

spindle fiberspindle fiber kinetochoreskinetochores

centriole

asterfibers

• Shortest phase

•• CentriolesCentrioles travel to the poles of the cell and anchor with aster aster fibersfibers.

•• ChromosomesChromosomes move to the metaphase platemetaphase plate(equatorial plateequatorial plate -center of cell).

MMEETTAAPPHHAASSEE

Aster fibers

Spindle fibers

Metaphase plate

MetaphaseMetaphase

metaphase plate

centrioles

spindle fibers

asterfibers

Centromeres separate and spindle fibersspindle fiberscontract.

Sister chromatidsSister chromatidsseparate and move apart.

After separation, chromatidschromatids are now considered chromosomeschromosomes.

AANNAAPPHHAASSEE

Problem solving: How does a chromosomemove.

AnaphaseAnaphase

No longer sister chromatidssister chromatids, now chromosomeschromosomes

centriolesspindle fibers

asterfibers

AANNAAPPHHAASSEE

AANNAAPPHHAASSEE

TTEELLOOPPHHAASSEE

• Nuclear membrane and nucleolus reappear.

• Chromosomes uncoil to chromatin.

• In the end, two genetically identical nuclei are present

• Cleavage furrow develops in animal cells. Cell platedevelops in plants.

cell plate

TTEELLOOPPHHAASSEE

cleavage furrow (cytokinesis)

nuclear membrane reforming

nucleolus reappears

CytokinesisCytokinesis-- after Mitosisafter Mitosis

• Cytoplasmic division

•• Cell plate Cell plate complete in plantsplants

• In the end, two separate daughter cells produced with single nucleus.

cell plate

CCYYTTOOKKIINNEESSIISS

What phase is show in each micrograph above?

• If a plant cell undergoes mitosis, but no cell plate if formed, what would be the result?

• Corn cells have 20 chromosomes. If it is dividing mitotically, how many chromosomes will be present at prophase, metaphase and anaphase?

• A biologist studying corn roots (normally 20 chromosomes) locates one in late telophase with only 19 chromosomes. How might this have occurred?

Knowing When to Start/Stop

• Suppose you had a paper cut on your finger. Although the cut may have bled and stung a little, after a few days, it will have disappeared, and your finger would be as good as new.

1. How do you think the body repairs an injury, such as a cut on a finger?

2. How long do you think this repair process continues?3. What do you think causes the cells to stop the repair

process?

PROBLEM SOLVINGPROBLEM SOLVING

• Contact Inhibition

A sample of cytoplasmis removed from a cellin mitosis.

The sample is injectedinto a second cell inG2 of interphase.

As a result, the second cell enters mitosis.

Knowing when to

stop• Phases• Check Points-

• What does G0 mean?

• What does this mean for the cell?

PPRROOBBLLEEM M

SSOOLLVVIINNGG

PROBLEM SOLVINGPROBLEM SOLVING

Stem Cells

• http://www.sumanasinc.com/webcontent/animations/generalscience.html

• http://www.dnalc.org/ddnalc/resources/stem_cells.html

PROBLEM SOLVINGPROBLEM SOLVING

Stem Cells-

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SSOOLLVVIINNGG

PROBLEM SOLVINGPROBLEM SOLVING

PROBLEM SOLVINGPROBLEM SOLVING

PROBLEM SOLVINGPROBLEM SOLVING